Abstract
The mirobial decomposition process of househole waste, mainly food waste, is considered an environmentally friendly way to treat organic wastes. However, there are some problems which often occur, such as low conversion rate and bad smell generation, especially in the early stage of continuous operation systems. Rice bran has been known empirically as an acclerator or improving material for the microbial decomposition process of organic wastes. Unfortuantely, little information about the detailed findings has been obtained so far.
 
 This study intended to analyze the effect of rice bran as an activating agent in organic waste decomposition in order to minimalize the problems. Firstly, the effect of rice bran was confirmed. Reactor weight, temperature, moisture content, pH, and microbe number were measured and used as the parameters to confirm the effect of rice bran addition in the decomposition process. It was observed that the total waste reduction during the process was larger in the case of rice bran addition than that of the blank, i.e. without rice bran addition. The other parameters also showed similar tendencies, indicating that rice bran is surely capable of activating the decomposition process. Then, the growth accelerating effect for microorganisms in the composting process was examined by a cultivation test using trypticase-soy liquid medium. The microbe number in the medium with rice bran addition was higher than the medium without rice bran.
 
 Secondly, the factors contributing this effect were searched. Although we could narrow down the number of candidate constituent, among them magnesium was one of the major candidates, the precise identification was not possible, possibly because the effect of each nutrient on the microbes varies depending on the kind of microbial strain, and not a single but a combination of multiple nutrients may cause this effect. However, it was confirmed as a whole that rice bran shows a good influence on the growth of many micorbes in the composting process and accelerates the performance of decomposition. 
Highlights
Household waste disposal has been a study topic for several decades (Haug, 1993: Pearce and Brisson, 1995: U.S EPA, 1995: Morgan, 2006)
The temperature of normal composting rose in the second day and was not as high as rice bran addition composting
It was observed that rice bran addition in the composting process could activate the early stage of the decomposition process
Summary
Household waste disposal has been a study topic for several decades (Haug, 1993: Pearce and Brisson, 1995: U.S EPA, 1995: Morgan, 2006). The problems are its large amount in total domestic waste and its difficulty to be treated (Matsuda, 2016). Most domestic waste in Japan is treated with an incineration process, which has a financial burden (Maruchi and Matsuda, 2016). Food waste has been considered as the major content in household waste (Walsh and Jones, 1991). Reflecting on its large amount in household waste and the organic content, the microbial garbage treatment system is considered as an alternative way for household waste disposal (Matsuda et al, 2017). In the development of this system, another problem occurred, such as low decomposition rate in the early stage of the process and decreasing of decomposition rate when overloading phenomena occurred (Maruchi and Matsuda, 2016)
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